Growing up Too Fast?

I was always a big kid. I remember how the stalls in the restroom were shorter than me and I could see into everyone else's stalls! I had to bend down in fifth grade to use the mirrors...I was just taller than the other kids. When I was like six, I looked more like and eight or nine year old and so when I acted like a six year old people took offense sometimes. I had a sister but she was handicapped and didn't speak so I grew up talking to adults and had a wide vocabulary at a young age. I was also a feisty kid, not really from TV, just the way I am ;) I would just correct her about something as things come up and give her attention, tell her how pretty she looks etc. It is hard to be larger than kids your age, as it is tough I think to be the smallest in the class as well. That tough exterior may be the outcome of developing a thick skin to handle all the comments she gets about herself, not only from children unfortunately. I would just treat her like a rambunctious four year old.

Stop letting her watch tv that is for older kids. And teach her to be nice, not bossy.

My daughter is 6.5 yrs old, in first grade, and could pass for 8/9 3rd grader. The bossy and "savvy" part is probably the problem, not her height.

Well, since it's not your child, there's not really anything you can do, unless of course your friend is actually looking for the advice. If she is, the first thing I'd suggest is not to allow a preschooler to watch t.v. shows that are about teenagers. Young kids pick that attitude up awfully fast. Shows like Hannah Montana and iCarly are not for young children, they are shows about high schoolers. If you don't want a 5 year old acting like a high schooler, don't set those role models.
It would also be helpful if when the child is being bossy, that either the child she is talking to tells her, "I don't want to play with you because you're being bossy. I'm going to play with Emma instead. She's nice" or for the parent or teacher to point out that the reason the other kid went to play with someone else is because this kid was trying to dictate all the rules, tell everyone what to do, and tell her how to be a good friend. Role playing games might be good too.

This is not your child, right?

All you can do is enforce your house rules at your house: take turns, play nice or off you go!

If she gets away with it at home, she'll think she can get away with it elsewhere. If you don't like her behavior, call her on it when she's at your house.
If you don't like how she treats your child, call her on it when they are playing together. You can't change how others parent, but you can change how your children perceive her behavior.
LBC